Apparatus and method for drying washed objects

ABSTRACT

An apparatus and a method for drying washed objects being capable of drying the objects in a reduced period of time, effectively preventing contamination of the objects, and preventing energy loss are provided. The apparatus for drying washed objects includes a drying tank having an opening on the upper portion thereof so that the washed objects can be placed or taken out from above, and a rinsing tank formed integrally with the drying tank, and is capable of being sealed hermetically by closing the openable and closable lid. The drying tank includes a mist-straightening vane for supplying organic solvent mist at normal temperatures to the washed objects, so that the washed objects are dried by organic solvent mist emitted from the mist-straightening vane.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an apparatus and a method fordrying washed objects, and more specifically, to an apparatus and amethod for drying washed objects being suitable for washing, rinsing,and drying substrates of semiconductor wafers.

[0003] 2. Description of the Related Art

[0004] Heretofore, removal of moisture entered in trenches is animportant factor in drying of miniaturized washed objects such as wafersafter washing of precision substrates, and thus a drying apparatus usingorganic solvent vapor is employed. An apparatus shown in FIG. 1 is knownas a drying apparatus using organic solvent vapor.

[0005] The drying apparatus 1 includes, as shown in FIG. 1, a dryingtank 2 being box-shape having an opening on top thereof in crosssection, a heating device (heater) 3 mounted on the bottom surface 2 aof the drying tank 2, a cooling coil 4 provided on the upper part of thedrying tank 2, a solvent trap 5 provided downwardly of the cooling coil4, a wafer placing table 7 disposed in the drying tank 2 for placing awafer 6 as a washed object thereon, and a solvent pooling section 8disposed downwardly of the wafer placing table 7.

[0006] The drying apparatus 1 heats organic solvent 9 charged into thedrying tank 2 to a boiling point by the heater 3 and generates organicsolvent vapor in the upper portion thereof. A wafer 6 already washed andrinsed with water is then inserted and arranged in the vapor in thedrying tank 2. Condensation of organic solvent occurs on the surface ofthe wafer 6 that is inserted and arranged in the drying tank 2, and thenmoisture attached on the surface of the wafer 6 is replaced by organicsolvent which is more likely to evaporate, whereby the wafer 6 isprogressively dried. The wafer 6 in the organic solvent vapor isgradually increased in temperature to an evaporating point (boilingpoint), and then is taken out of the mist atmosphere, where attachedsolvent component rapidly evaporates due to its low latent heat, to becompletely dried.

[0007] The organic solvent heated and vaporized by the cooling coil 4disposed on the upper part of the drying tank 2 is condensed and droppedin the solvent trap 5 for recovery and reusing. Likewise, solventincluding moisture dropped from the wafer 6 is also recovered in thesolvent pooling section 8.

[0008] The drying apparatus 1 in the related art demands attention toflames since organic solvent is heated by the heater 3, and consumes alot of energy because it carries out heating and cooling. In addition,it requires a significant period of time until a vapor layer is formedby being heated by the heater 3, and consumes a large quantity oforganic solvent due to evaporation. Further, when the washed objectscome in contact with the mist layer, heat of vapor (gas phase) isabsorbed by the washed object, thereby causing abrupt change in phase(gas phase to liquid phase) and reducing the vapor layer. Consequently,the washed object is exposed to the atmosphere, which may easily resultsin contamination, insufficient drying, and so on.

SUMMARY OF THE INVENTION

[0009] Accordingly, it is an object of the present invention to providean apparatus and a method for drying washed objects being capable ofdrying the washed objects in a reduced period of time, effectivelypreventing contamination of the objects, and preventing energy loss.

[0010] The apparatus for drying washed objects according to theinvention includes a drying tank in which organic solvent mist isgenerated and supplied to washed objects therein, wherein the dryingtank includes a mist-straightening vane for supplying organic solventmist to the washed objects.

[0011] The mist-straightening vane of the apparatus for drying washedobjects according to the invention is provided on the side wall of thedrying tank, and is provided with a plurality of fine openings on thesurface for emitting organic solvent mist at the position upwardly of afluid spray nozzle away from a prescribed distance S, so that a portionof organic solvent mist that passed through the opening out of the wholepart of organic solvent mist emitted from the fluid spray nozzle isindirectly emitted.

[0012] The fluid splay nozzle of the apparatus for drying washed objectsaccording to the invention can emit two or more different types of fluidsimultaneously.

[0013] Fluid emitted from the fluid spray nozzle of the apparatus fordrying washed objects according to the invention includes organicsolvent mist and inert gas.

[0014] The configuration of the opening of the apparatus for dryingwashed objects according to the invention is chamfered configuration.

[0015] The apparatus for drying washed objects according to theinvention includes a drying tank having an opening on top thereof sothat the washed objects can be placed or taken out from above and arinsing tank formed integrally with the drying tank, and is capable ofbeing sealed hermetically by closing the openable and closable lid, andthe drying tank includes a mist-straightening vane for supplying organicsolvent mist to the washed objects.

[0016] The drying tank of the apparatus for drying washed objectsaccording to the invention includes an overflow tank formed on top ofthe rinsing tank integrally for overflowing deionized water to besupplied into the rinsing tank, and a channel for drainage from theoverflowing tank is grounded.

[0017] The apparatus for drying washed objects according to theinvention includes cradles for placing and holding washed objects in thedrying tank and in the rinsing tank, and the cradle can be moved upwardand downward by a hoisting mechanism and can be stopped in a state inwhich a part of the washed object is in contact with the fluid leveldirectly or indirectly.

[0018] The portion of the washed object that is immersed into the fluidlevel of the rinsing tank of the apparatus for drying washed objectsaccording to the invention is the portion other than the patternedsurface.

[0019] A method for drying washed objects according to the invention isa method for drying washed objects for performing drying by the use of adrying apparatus including a drying tank having an opening on topthereof so that washed objects can be placed or taken out from above,and a rinsing tank formed integrally with the drying tank, and iscapable of being sealed hermetically by closing an openable and closablelid, comprising the steps of moving a cradle for placing and holdingwashed objects upward and downward by a hoisting mechanism after thewashed object was rinsed in the rinsing tank and stopping the same in astate in which a part of the washed object is in contact with the fluidsurface directly or indirectly, performing drying process by emittingorganic solvent mist to the washed object from a fluid spray nozzleprovided on a mist-straightening vane and emitting the same in turn fromthe mist-straightening vane indirectly, draining deionized water afterthe drying step, and performing quick drying process by supplying inertgas at a high temperature into the drying tank after the draining step.

[0020] In a method for drying washed objects according to the invention,the washed object is wet when the washed object is drawn up from therinsing tank by the hoisting mechanism.

[0021] In a method for drying washed objects according to the invention,the inert gas is nitrogen gas (N₂) at normal temperatures or heatednitrogen gas (N₂).

[0022] In a method for drying washed objects according to the invention,an organic solvent for generating the mist of organic solvent isselected from alcohols, ketones, or ethers having water solubility andcapability of lowering surface tension of deionized water with respectto the substrate.

[0023] In a method for drying washed objects according to the invention,the diameter of organic solvent mist emitted indirectly from themist-straightening vane is not more than 20 μm.

[0024] In a method for drying washed objects according to the invention,the organic solvent can be heated to temperatures within the range of 5°C. to 80° C. when it is IPA (Isopropyl alcohol).

[0025] In a method for drying washed objects according to the invention,rinsing water for performing rinsing operation in the rinsing tank ishydrogenated water.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a drawing showing a drying apparatus in the related art;

[0027]FIG. 2 shows a drying apparatus according to an embodiment of theinvention partially in cross section;

[0028]FIG. 3 is an explanatory drawing illustrating a state in whichorganic solvent mist is emitted indirectly by the use of amist-straightening vane;

[0029]FIG. 4 is an explanatory drawing illustrating the diameter oforganic solvent mist emitted from the mist-straightening vane and theemitting state;

[0030]FIG. 5(a) and FIG. 5(b) are enlarged cross sectional views showingthe configurations of the opening on the mist-straightening vane;

[0031]FIG. 6 is a drawing showing a state of transferring particles as aresult of being dried using Marangoni Effect, that is, Marangoni Drying,after being etched by DHF (HF/H₂O) (diluted hydrofluoric acid);

[0032]FIG. 7 is a graph of the increasing amount of particles inMarangoni Drying, illustrating the result after performing the steps ofrinsing with deionized water→drying, and the result after performing thesteps of etching with DHF (HF/H₂O) (diluted hydrofluoric acid)→rinsingwith deionized water→drying;

[0033]FIG. 8 is a drawing for comparing the amount of increase inparticles in Marangoni Drying and drying according to the invention;

[0034]FIG. 9 is an explanatory drawing showing the drying process in adrying method according to the invention;

[0035]FIG. 10 is a time chart of the drying process according to theinvention;

[0036]FIG. 11 is an enlarged explanatory drawing of a state shown inFIG. 9(e);

[0037]FIG. 12 is an explanatory drawing illustrating the amount ofelectrostatic charge on the surface of the wafer shown in FIG. 11;

[0038]FIG. 13 is a drawing showing a state in which the diameter and thenumber of the particles of organic solvent mist M are measured by theuse of a Phase Doppler Particle Analyzer for five minutes when themist-straightening vane is used;

[0039]FIG. 14(a) is a drawing showing results of measurement in theexperiment conducted in conjunction with FIG. 13, and FIG. 14(b) is adrawing showing results of measurement of the diameter and the number ofparticles of organic solvent mist M without using the mist-straighteningvane shown in FIG. 13.

[0040]FIG. 15 is a diagrammatic sketch of a state in which electrostaticcharge is being removed;

[0041]FIG. 16 is a graph of the thickness of oxidized film on thesurface of the silicon measured after being etched by DHF (HF/H₂O)(diluted hydrofluoric acid) and being rinsed with hydrogenated waterwhich is obtained by adding hydrogen water to rinsing water in therinsing tank by the use of the drying apparatus according to theinvention, and then performed the drying process; and

[0042]FIG. 17 is a drawing showing another embodiment of the dryingapparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] Referring now to the drawings, an embodiment of a dryingapparatus and a drying method according to the invention will bedescribed. FIG. 2 is a drawing showing a drying apparatus according toan embodiment of the invention partly in cross section.

[0044] As shown in FIG. 2, the drying apparatus 11 includes a dryingtank 30, a rinsing tank 40, and a plumbing system 50. The drying tank 30is provided on top of the rinsing tank 40 integrally therewith. Thedrying tank 30 is open on top thereof and thus the wafer W as washedobjects can be placed or taken out from above, and is capable of beingsealed hermetically by closing an openable and closable lid 31. In otherwords, a lid packing 39 completely prevents outside air from enteringtherein. The openable and closable lid 31 is opened and closed bysliding movement thereof via a guiding mechanism, which is not shown inthe figure, in the vertical direction with respect to the plane of FIG.2. FIG. 2 shows the closed state.

[0045] The drying tank 30 and the rinsing tank 40 are constructed ofmembers having non-conductive properties and corrosion resistanceproperties, and are box-shape opening on top in cross section. Therinsing tank 40 is slightly smaller than the drying tank 30, and theupper portion of the rinsing tank 40 is placed into the lower portion ofthe drying tank 30. It is for allowing deionized water in the rinsingtank 40 to overflow.

[0046] As shown in FIG. 2, mist-straightening vanes 32 for supplyingorganic solvent mist, which is IPA in this embodiment, indirectly to thewafer W as a washed object are provided on both sides of the side wallof the drying tank 30 so as to sandwich the outer peripheral surface ofthe wafer W. The wafer W in the drying tank 30 is, as shown in FIG. 2,substantially circular (a part of the outer periphery is cut out to forman orientation flat), and a plurality of wafers W are disposed inparallel at regular intervals in the vertical direction with respect tothe plane of the figure. Generally, when they are semiconductor wafers,for example, 100 pieces of wafers measuring 8 inches in diameter may beplaced, though the number and the diameter may be selected asappropriate. These wafers Ware placed on the cradle 33 having foursupporting members in this embodiment. In this embodiment, the wafer Wis assumed to have 12 inches in diameter. As shown in FIG. 2, the cradle33 is capable of moving upward and downward between the rinsing tank 40and the drying tank 30 by the aid of a hoisting mechanism, which is notshown.

[0047] The mist-straightening vane 32 is formed entirely of a laterallyelongated rectangular solid as shown in FIG. 3, and has a width thatenable itself to supply organic solvent mist M, which is IPA in thiscase, to the main surfaces of the plurality of wafers W simultaneously.Formed on the surface 32F of the mist-straightening vane 32 positionedon the side of the peripheral surface of the wafer W are a plurality offine openings 32 a. The size of the opening 32 a is approximately 5 mmin this embodiment. The openings 32 a are, as shown in FIG. 4 as well,not formed on the area from the lower end of the mist-straightening vane32 (the position on which a fluid spray nozzle 34 is to be mounted) tothe point at a distance S. The organic solvent mist M of IPA is, asshown in FIG. 2 through FIG. 4, supplied by a sufficient amount in theform of high-density mist M of an organic solvent (two different typesof fluid are supplied in this embodiment) from the fluid spray nozzle 34mounted at the lower portion of the mist-straightening vane 32, filledinside the mist-straightening vane 32, and supplied from the openings 32a indirectly to the wafer W. The diameter of the emission aperture ofthe fluid spray nozzle 34 is approximately 1 mm. The organic solvent forgenerating the organic solvent mist is selected from alcohols, ketones,or ethers having water solubility and capability of lowering surfacetension of the deionized water with respect to the substrate.

[0048] Referring now to FIG. 4, the change in the state of the organicsolvent mist M in this embodiment will be described in detail. Theorganic solvent mist M emitted from an emission aperture at the tip ofthe fluid spray nozzle 34 and in the region a, that ranges from thelower end to the position at a distance S (about 100 mm in thisembodiment), is filled with organic solvent mist ML of at least 20 μm.On the other hand, the region b upwardly of the region a is filled withmixture of organic solvent mist ML of at least 20 μm and organic solventmist MS of less than 20 μm. The mixed organic solvent mist ML and MS arestraightened at the openings 32 a on the mist-straightening vane 32, andonly the organic solvent mist MS passes therethrough and is supplied tothe wafer W. The organic solvent mist ML of at least 20 μm is condensedinside the mist-straightening vane 32 and discharged from a dischargeport 32 b shown in FIG. 3.

[0049]FIG. 13 is a drawing showing a state in which the diameter and thenumber of particles of organic solvent mist M when using themist-straightening vane 32 are measured by the use of a Phase DopplerParticle Analyzer for five minutes, FIG. 14(a) is a drawing showingresults of experiment conducted in conjunction with FIG. 13, and FIG.14(b) is a drawing showing results of measurement of the diameter andthe number of particles of the organic solvent mist M without using themist-straightening vane shown in FIG. 13. The lateral axes in FIG. 14(a)and FIG. 14(b) represent the diameter of the particle of the mist (μm)and the vertical axes thereof represent the number of mist particles.

[0050] As shown in FIG. 13 and FIG. 14, when the mist-straightening vane32 was not used, the mist diameter showing the peak of the number ofmist particles was in the vicinity of 8 μm, and the average mistparticle diameter was 11.5 μm. Many large particles measuring at least10 μm in diameter were also detected.

[0051] On the other hand, when the mist-straightening vane 32 was used,the mist diameter showing the peak of the number of mist particles wasin the vicinity of 5 μm, and the average mist particle diameter was 6.4μm. Large particles measuring at least 10 μm in diameter were foundlittle or nothing.

[0052] As is described thus far, the invention is contemplated based onthe fact that it is important to supply organic solvent mist M uniformlyto the space between the wafers W in order to dry a plurality of wafersW simultaneously, and thus organic solvent mist M having smallerdiameter is more preferable. It is because the particles of organicsolvent mist M having smaller diameter can be gasified easily incomparison with the particles having larger diameter, and thus the rateof diffusion in the air increases. Organic solvent mist Ma shown in FIG.4 is in the state of being gasified.

[0053] Therefore, according to the invention, organic solvent mist M ofIPA is indirectly emitted by the use of the mist-straightening vane 32without heating for generating organic solvent mist M as in the relatedart, whereby high-securities are ensured and organic solvent mist M canbe supplied immediately, thereby improving operating efficiency of theentire apparatus.

[0054]FIG. 5(a) and FIG. 5(b) are enlarged cross sectional view showingthe configuration of the opening 32 a on the mist-straightening vane 32.

[0055] The semiconductor wafer W and organic solvent mist M of IPA havea property that is apt to be charged. Therefore, in the case where theedge portion of the opening 32 a is acutely angled as shown in FIG.5(a), electrostatic charge causes concentration of electric field, andthus increases probability of discharge, which results in charging ofthe wafer W by induction. Therefore, in order to prevent such acondition, the edged portion in this embodiment is not formed into anacutely angled edge as shown in FIG. 5(b), but chamfered to preventelectric field from concentration when being charged, and to reduce theprobability of occurrence the discharging phenomenon. In thisembodiment, other chamfered configuration may be employed as far as itcan reduce the probability of occurrence of the discharging phenomenon.The organic solvent mist is also referred to as IPA mist.

[0056] As shown in FIG. 2, the drying tank 30 is provided with a exhaustport 36 at the upper portion thereof and a nitrogen gas supply port 37for supplying nitrogen gas (N₂).

[0057] The rinsing tank 40 is supplied with deionized water through thedeionized water supplying nozzle 41 for supplying deionized water asshown in FIG. 2. When deionized water supplied into the rinsing tank 40reaches to a certain level, it is stored temporarily in an overflow tank42 shown in FIG. 2 and then is overflowed through the channel with adrain valve 52. The channel with the drain valve 52 is grounded. In sucha situation, a gaseous phase portion 35 is formed in the drying tank 30.The rinsing tank 40 is provided with a drain valve 43 for drainingdeionized water at the center on the bottom thereof, so that deionizedwater in the tank is drained through the drainage duct when the drainvalve 43 is opened.

[0058] The plumbing system 50 to be connected to the drying tank 30 andrinsing tank 40 will be described below.

[0059] The plumbing system 50 includes (1) a channel for supplyingnitrogen gas (N₂) to the nitrogen gas supply port 37, (2) a channel forsupplying two types of fluids, IPA as a organic solvent and nitrogen gas(N₂), to the fluid spray nozzle 37, (3) a channel for exhausting airfrom the drying tank 30, (4) a channel for supplying deionized waterinto the rinsing tank 40, (5) a channel for drainage from the overflowtank 42, and (6) a channel for draining deionized water in the rinsingtank 40. Control of the plumbing system 50 is performed by control unitwhich is not shown in the figure.

[0060] (1) In the channel for supplying nitrogen gas (N₂) to thenitrogen gas supply port 37, nitrogen gas (N₂) at ordinary temperaturessupplied when the valve 53 is in the opened state (ON) is heated by aheater 54 and supplied to the nitrogen gas supply port 37 through afilter 55. Nitrogen gas (N₂) at high temperatures heated by the heater54 is used for quickly drying the wafer W as a washed object in thedrying tank 30. In the cannel for supplying nitrogen gas (N₂) to thenitrogen gas supply port 37, as shown in FIG. 2, when the aforementionedvalve 53 is in the opened state (ON), the other valve 56 is in theclosed state (OFF). In contrast to it, when the valve 53 is in theclosed state (OFF), the valve 56 is in the opened state (ON), andnitrogen gas (N₂) at ordinary temperatures is supplied to the dryingtank 30 through the filter 55. Even when the wafer W as a washed objectdoes not exist in the drying tank 30, clean nitrogen gas (N₂) atordinary temperatures is supplied into the drying tank 30 so that thegaseous phase portion 35 is completely filled.

[0061] The valve 53, the valve 56, and the heater 54 can be controlledby the control unit which is not shown, so that switching of the valve53 and the valve 56, and the temperature of the heater 54 arecontrolled.

[0062] (2) The channel for supplying two different types of fluid, IPAas an organic solvent and nitrogen gas (N₂), to the fluid spray nozzle37 includes an IPA tank 59 for storing IPA, a pump 60 for supplying IPAfrom the IPA tank 59, a filter 61 for cleaning supplied IPA, a valve 62,a valve 63, an IPA heater 67 for heating IPA, and a valve 57 forsupplying nitrogen gas (N₂), and a filter 58. Two types of fluid, IPA asan organic solvent and nitrogen gas (N₂), are supplied to the fluidspray nozzle 34 simultaneously. Nitrogen gas (N₂) is for securingsafety. Such control is performed by the control unit which is not shownin the figure as described above.

[0063] (3) The channel for exhausting air from the drying tank 30 is forsucking and exhausting air from the exhaust port 36 with the valve 64opened (ON).

[0064] (4) The channel for supplying deionized water into the rinsingtank 40 is for supplying deionized water from the deionized watersupplying nozzle 41 with the valve 51 opened (ON).

[0065] (5) The channel for drainage from the overflow tank 42 is fordraining deionized water overflowed from the rinsing tank 40 and IPAwhich is a dissolved organic solvent through the drain valve 52.

[0066] (6) The channel for draining deionized water in the rinsing tankemploys a drain valve 43.

[0067] The drying method using the drying apparatus of the invention ischaracterized by being a drying method which does not utilize MarangoniEffects as in the case shown in FIG. 6. FIG. 6 is a drawing showing astate of transferring particles as a result of being dried usingMarangoni Effects, that is, Marangoni Drying, after being etched by DHF(HF/H₂O) (diluted hydrofluoric acid), and FIG. 7 is a graph of theincreasing amount of particles in Marangoni Drying, illustrating theresult after performing the steps of rinsing with deionizedwater→drying, and the result after performing the steps of etching withDHF (HF/H₂O) (diluted hydrofluoric acid)→rinsing with deionizedwater→drying. The concentration of IPA in FIG. 6 is CI>CII, and thesurface tension is rI<rII. When the concentration of IPA is CII=CIII,the surface tension is rII=rIII. C represents the concentration of IPA,r represents the surface tension, and Roman numbers I to III representthe position shown in FIG. 6.

[0068] As is clear from FIG. 6, IPA gas (not IPA mist) is suppliedbetween a bear wafer and a wafer with an oxidized film, and whendeionized water is withdrawn downward in this state, water is apt to bestuck on the bear wafer facing toward the wafer with an oxidized film byMarangoni Force, and the particles are also apt to be stuck on the bearwafer. Therefore, as is clear from FIG. 7, the number of particlesincreases abruptly when dried by Marangoni Drying after being etched byDHF (HF/H₂O) (diluted hydrofuoric acid).

[0069]FIG. 8 is a graph for comparing the drying method using the dryingapparatus according to the invention, and the drying method usingMarngoni Effects, and an object of the invention is to provide a dryingmethod in which increase in the number of particles due to MarangoniDrying after being etched by DHF (HF/H₂O) (diluted hydrofuoric acid) asshown in FIG. 6 and FIG. 7 is prevented.

[0070] Referring now to FIG. 9 through FIG. 12, the drying methodaccording to the invention will be described. FIG. 9 is an explanatorydrawing showing the drying process in the drying method according to theinvention, FIG. 10 is a time chart of the drying process according tothe invention, FIG. 11 is an enlarged explanatory drawing of a stateshown in FIG. 9(e), and FIG. 12 is an explanatory drawing illustratingthe amount of electrostatic charge on the surface of the wafer shown inFIG. 11.

[0071] (1) Drying Step Shown in FIG. 9(a)

[0072]FIG. 9(a) shows a state where no wafer W exists in the dryingapparatus 11. As shown in the step 1 in FIG. 10, in a state in which theopenable and closable lid 31 is closed, and deionized water is suppliedfrom the deionized water supply channel (4) to the rinsing tank 40 foroverflow rinsing, nitrogen gas (N₂) is supplied from the nitrogen gas(N₂) supply channel (1) through the valve 56, the filter 55, and thenitrogen gas supply port 37 to the drying tank 30, and simultaneously,air is sucked and exhausted from the exhaust channel (3) with the valve64 opened, and IPA is circulated in the IPA supply channel (2) with thevalve 63 closed and the valve 62 opened. At this time, the cradle 33 islowered into the rinsing tank 40.

[0073] (2) Drying Step Shown in FIG. 9(b)

[0074] The openable and closable lid 31 of the drying tank 30 is openedand a washed object such as a wafer W that is washed or rinsed isstored, placed and supported on the cradle 33 by means of a carryingunit, not shown. The openable and closable lid 31 is constructed to beopenable and closable automatically or manually when the wafer was awashed object is loaded in or unloaded from the drying tank 30 or therinsing tank 40. As shown in the step 2 in FIG. 10, all the points suchas overflow rinsing, supply of nitrogen gas (N₂), suction exhaust, andIPA circulation are identical to FIG. 9(a) other than the fact that theopenable and closable lid 31 is opened and the cradle 33 is movedupward.

[0075] Subsequently, when the washed object such as a wafer W is placedon the cradle 33, the carrying unit, not shown, is retracted from thedrying tank 30, the openable and closable lid 31 is closed, and thecradle 33 is lowered into the rinsing tank 40 together with the wafer W.

[0076] (3) Drying Step Shown in FIG. 9(c)

[0077]FIG. 9(c) shows a rinsing step using deionized water performed inthe rinsing tank 40. The valve 51 on the channel (4) shown in FIG. 2 isopened, and deionized water is supplied from the deionized watersupplying nozzle 41 for overflow rinsing. The openable and closable lid31 is closed, the cradle 33 is in the lowered state, and the states ofsupply of nitrogen gas (N₂), suction exhaust, IPA circulation areidentical to the case shown in FIG. 9(b). The overflow rinsing isperformed at a rate of about 30 litters/min for about 60 seconds.

[0078] (4) Drying Step Shown in FIG. 9(d)

[0079]FIG. 9(d) shows a state in which the cradle 33 on which the waferW is placed in the rinsing tank 40 is moved upward after overflowrinsing in the step 3 in FIG. 10 is finished. As is clear from FIG. 10,the process in the step 4 is identical to that in the step 3 except forupward movement of the cradle 33. The period of time required for movingthe cradle 33 upward is approximately 30 seconds as shown in the step 4in FIG. 10. The upward movement of the cradle 33 will be stopped in astate in which the lower surface of the wafer W is slightly immersed inthe fluid surface in the rinsing tank 40, as is clear from FIG. 9(e).Though the stop position of the cradle 33 is controlled by a controlunit which is not shown in the figure, the stop position is set inadvance. When the washed object is a wafer W, since the wafer W isprovided with a pattern on the surface thereof, it is stopped in a statein which the portion of the wafer W in the vicinity of the outerperiphery thereof, which is not formed with a pattern, comes intocontact with the fluid surface. In this case, the wafer W as a washedobject is still wet when it is drawn upward from the rinsing tank 40 bythe hoisting mechanism.

[0080] Though a state in which the lower surface of the wafer W isdirectly in contact with and immersed into the fluid surface in therinsing tank 40 has been described, the inventor verified thatelectrostatic charge can be removed by bringing the wafer W intoindirect contact with the fluid surface in the rinsing tank 40 by theuse of a draining rod for securing indirect contact between the wafer Wand rinsing water as shown in FIG. 15, and allowing water to drop viathe draining rod. FIG. 15 is a diagrammatic sketch of a state in whichelectrostatic charge is being removed.

[0081] (5) Drying Step Shown in FIG. 9(e)

[0082]FIG. 9(e) corresponds to the step 5 in FIG. 10, in which the valve62 shown in FIG. 2 is closed and the valve 63 is opened, and the valve57 is opened to supply two types of fluid, IPA as an organic solvent andnitrogen gas (N₂), from the fluid splay nozzle 34 into the drying tank30. Such IPAmist supply continues for approximately 120 seconds as shownin FIG. 10. In this case, the IPA heater 67 can be heated to thetemperatures in the range between 5° C. and 80° C., and the IPA heater67 is turned ON when supplying IPA mist.

[0083] As shown in FIG. 11, the IPA mist atmosphere in the drying tank30 is apt to become positively charged, and thus the wafer W is apt tobe charged as well. Accordingly, in the drying method of the invention,as shown in FIG. 11, residual water on the wafer W with IPA mistdissolved therein runs along the surface on the wafer W downwardly anddrops into deionized water in the rinsing tank 40 and dissolves therein.Since overflow rinsing is performed as is clear from the step 5 in FIG.10, the overflow tank 42 is grounded via a drainage channel (FIG. 2 (5))and thus positive electrostatic charge is removed.

[0084]FIG. 12(a) is a graph illustrating measured amount ofelectrostatic charge on the wafer surface when it is dried withoutimmersing the lower surface of the wafer W in the fluid surface in therinsing tank 40 according to a method other than the invention. Suchmeasurement is performed during the drying process shown in FIG. 9(e)and in the step 5 in FIG. 10. Change in the amount of electrostaticcharge shown in FIG. 12(a) is caused by the phenomenon in whichelectrostatic charge is temporarily removed from the wafer W whenresidual water on the surface of the wafer W and IPA drop into rinsingwater in the rinsing tank 40.

[0085]FIG. 12(b) is a graph illustrating measured amount ofelectrostatic charge on the surface of the wafer when the wafer W isdried with the lower surface of the wafer W directly immersed into thefluid surface in the rinsing tank 40 according to the invention. Suchmeasurement is performed during the drying process shown in FIG. 9(e)and in the step 5 in FIG. 10, and it is recognized that the amount ofelectrostatic charge on the surface of the wafer is removed according tothe invention. The same effects can be obtained when removal ofelectrostatic charge is performed without immersing the lower surface ofthe wafer W directly into the fluid surface in the rinsing tank 40, butperformed indirectly by the use of drainage rod as is described inconjunction with FIG. 15.

[0086] (6) Drying Step Shown in FIG. 9(f)

[0087]FIG. 9(f) shows a state in which the valve 63 shown in FIG. 2 isclosed, and the valve 62 in the same figure is opened to stop supply ofIPA mist and thus IPA is circulated. Subsequently, the drain valve 43 isopened to drain deionized water in the rinsing tank 40. The period oftime required for processing is approximately 10 seconds. As shown inthe step 6 in FIG. 10, nitrogen gas (N₂) is supplied through thenitrogen gas (N₂) supply channel (1), the valve 56, the filter 55, andthe nitrogen gas supply port 37 into the drying tank 30, and in theexhaust channel (3), the valve 64 is opened and thus sunction exhaust isbeing performed.

[0088] (7) Drying Step Shown in FIG. 9(g)

[0089]FIG. 9(g) corresponds to the step 7 in FIG. 10, and illustrates astate in which the valve 56 is closed to stop supply of nitrogen gas(N₂) at ordinary temperatures, the valve 53 is opened, and nitrogen gas(N₂) is heated by the heater 54 to supply nitrogen gas (N₂) at hightemperatures into the drying tank 30. The period of time required forsupplying nitrogen gas (N₂) at high temperatures is approximately 150seconds, and during which the surface of the wafer W in the drying tank30 is quickly dried.

[0090] (8) Drying Step Shown in FIG. 9(h)

[0091]FIG. 9(h) shows a state in which the valve 53 is closed and theheater 54 is turned off under the atmosphere of high-temperaturenitrogen gas (N₂) in the previous step, and then the valve 56 is openedto supply nitrogen gas (N₂), which is inert gas at ordinarytemperatures, into the drying tank 30 to return the interior of thedrying tank 30 to ordinary temperatures, which is so called “coolingdown”. The period of time required for this process is approximately 30seconds. The interior of the drying tank 30 is maintained in an inertgas atmosphere by nitrogen gas (N₂), which is an inert gas at ordinarytemperatures, being supplied from the nitrogen gas supply port 37, sothat the surface of the wafer, for example, a silicone (Si) can beprevented from reoxidization.

[0092] (9) Drying Step Shown in FIG. 9(i)

[0093]FIG. 9(i) shows a state in which the openable and closable lid 31is opened to carry the dried wafer W placed on the cradle 33 out of thedrying tank 30 with the carrying unit, not shown, as shown in the step 9in FIG. 10.

[0094] As is described above, the drying apparatus according to theinvention is constructed of the drying tank 30 and the rinsing tank 40,and thus the space can be saved. Further, since organic solvent mist isnot supplied in the step of drawing the wafer W up from the rinsing tank40 according to the invention, Marangoni Effects do not occur at theinterface between the wafer W and rinsing water in the rinsing tank 40.Therefore, particle transfer does not occur neither. In the dryingmethod according to the invention, gas at ordinary temperatures is usedas nitrogen gas (N₂), which is an inert gas in order to maintain theatmosphere at ordinary temperatures. Therefore, nitrogen gas (N₂) as aninert gas used in the step of vaporizing organic solvent (IPA) fordrying (the step 7 in FIG. 10) is preheated, because it enables quickdrying. Temperatures to be heated are preferably between 20° C. and 100°C. according to the exemplified experiment. However, gas at ordinarytemperatures, which is not heated, may be used depending on the type ofwashed objects. Though nitrogen gas (N₂) is used as an inert gas in thisembodiment, argon gas may be used as an alternative. Further more,according to the invention, adherence of particles from the wafer havingan oxidized film or a pattern may be prevented, and reoxidization of thesurface of the silicon (Si) can be prevented.

[0095]FIG. 16 is a graph of the thickness of oxidized film on thesurface of the silicon measured after being etched by DHF (HF/H₂O)(diluted hydrofluoric acid) and being rinsed with hydrogenated waterwhich is obtained by adding hydrogen water to rinsing water in therinsing tank by the use of the drying apparatus according to theinvention and then performed the drying process. The lateral axisrepresents rinsing time (min), and the vertical axis represents thethickness of natural oxidized film (angstrom).

[0096] As shown in FIG. 16, though the thickness of oxidized film formedon the surface of the silicon increases in accordance with the rinsingtime, the inventor verified that development of natural oxidized film issuppressed when rinsed with hydrogenated water in comparison with thecase of being rinsed with ultra pure water having an O₂ concentration of15 ppb. It is considered to be because bonding between silicon (Si) andhydrogen is promoted due to existence of hydrogen in rinsing water andthus bonding between silicon (Si) and oxygen is hindered. From thesereasons, using hydrogenated water which is obtained by adding hydrogenwater to rinsing water suppresses development of natural oxidized filmon the surface of the silicon and prevents formation of watermark.Therefore, with the drying apparatus and the drying method according tothe invention, hydrogenated water may be selected as rinsing water.

[0097] Referring now to FIG. 17, another embodiment of the dryingapparatus according to the invention will be described. Since basicconstructions and functions are substantially identical to the apparatusshown in FIG. 2, only the different points will be described.

[0098] As shown in FIG. 17, since the drying apparatus 30 has aconstruction that does not have the rinsing tank 40, it does not havethe overflow tank 42. Therefore, the drying apparatus shown in FIG. 17is intended to perform only drying operation for the wafer W as a washedobject which has rinsed already in the previous step.

[0099] According to the invention, particle transfer due to MarangoniForce does not occur, and oxygen is purged because an inert gasatmosphere is formed by nitrogen, whereby formation of watermark isprevented and improvement of productivity is realized. Further, sincethe process is performed in a sealed structure, contamination of thewashed object can be prevented.

[0100] As is described thus far, according to the present invention,since organic solvent mist is indirectly emitted, the diameter oforganic solvent mist can be reduced. Further, according to theinvention, particle transfer due to Marangoni Force does not occur, andoxygen is purged because an inert gas atmosphere is formed by nitrogen,whereby formation of watermark can be prevented and improvement ofproductivity is realized. Furthermore, since the process is performed ina sealed structure, contamination of the washed object can be prevented.

What is claimed is:
 1. An apparatus for drying washed objectscomprising: a drying tank in which organic solvent mist is generated andsupplied to washed objects therein; wherein said drying tank includes amist-straightening vane for supplying organic solvent mist to saidwashed objects.
 2. An apparatus for drying washed objects according toclaim 1, wherein said mist-straightening vane is provided on a side wallof the drying tank, and is provided with a plurality of fine openings onthe surface for emitting organic solvent mist at the position upwardlyof a fluid spray nozzle away from a prescribed distance S, so that aportion of organic solvent mist that passed through the opening out ofthe whole part of organic solvent mist emitted from the fluid spraynozzle is indirectly emitted.
 3. An apparatus for drying washed objectsaccording to claim 2, wherein said fluid splay nozzle can emit two ormore different types of fluid simultaneously.
 4. An apparatus for dryingwashed objects according to claim 2 or 3, wherein fluid emitted fromsaid fluid spray nozzle includes organic solvent mist and inert gas. 5.An apparatus for drying washed objects according to claim 2, wherein theconfiguration of said opening is chamfered configuration.
 6. Anapparatus for drying washed objects comprising: a drying tank having anopening on top thereof so that the washed objects can be placed or takenout from above; and a rinsing tank formed integrally with the dryingtank, and an openable and closable lid being capable of being sealedhermetically by being closed, wherein said drying tank includes amist-straightening vane for supplying organic solvent mist to the washedobjects.
 7. An apparatus for drying washed objects according to claim 6,wherein said drying tank includes an overflow tank formed on top of saidrinsing tank integrally for overflowing deionized water to be suppliedinto the rinsing tank, and a channel for drainage from the overflowingtank is grounded.
 8. An apparatus for drying washed objects according toclaim 6, wherein cradles for placing and holding washed objects areprovided in the drying tank and in the rinsing tank, and said cradle canbe moved upward and downward by a hoisting mechanism and can be stoppedin a state in which a part of the washed object is in contact with thefluid level directly or indirectly.
 9. An apparatus for drying washedobjects according to claim 8, wherein the portion of said washed objectthat is immersed into the fluid level of said rinsing tank is theportion other than the patterned surface.
 10. A method for drying washedobjects for performing drying by the use of a drying apparatus includinga drying tank having an opening on top thereof so that washed objectscan be placed or taken out from above, a rinsing tank formed integrallywith the drying tank, and an openable and closable lid being capable ofsealing hermetically by being closed, comprising the steps of: moving acradle for placing and holding washed objects upward and downward by ahoisting mechanism after the washed object is subjected to the rinsingprocess in the rinsing tank and stopping the same in a state in which apart of the washed object is in contact with the fluid surface directlyor indirectly, performing drying process by emitting organic solventmist to the washed object from a fluid spray nozzle provided on amist-straightening vane and emitting the same in turn from themist-straightening vane indirectly, discharging deionized water afterthe drying step; and performing quick drying process by supplying inertgas at a high temperature into the drying tank after the draining step.11. A method for drying washed objects according to claim 10, whereinsaid washed object is wet when the washed object is drawn up from therinsing tank by the hoisting mechanism.
 12. A method for drying washedobjects according to claim 10, wherein said inert gas is nitrogen gas(N2) at ordinary temperatures or heated nitrogen gas (N₂).
 13. A methodfor drying washed objects according to claim 10, wherein an organicsolvent for generating organic solvent mist is selected from alcohols,ketones, or ethers having water solubility and capability of loweringsurface tension of deionized water with respect to the substrate.
 14. Amethod for drying washed objects according to claim 10, wherein thediameter of organic solvent mist emitted indirectly from themist-straightening vane is not more than 20 μm.
 15. A method for dryingwashed objects according to claim 13, wherein the organic solvent can beheated to temperatures within the range of 5° C. to 80° C. when it isIPA.
 16. A method for drying washed objects according to claim 10,wherein rinsing water for performing rinsing operation in the rinsingtank is hydrogenated water.